1. Field of the Invention
The invention relates to an electromagnetic injection valve or injector, preferably but not exclusively for use in association with an electronic unit controlling the supply of fuel to an internal combustion engine. More specifically, the invention relates to an injector which, by means of an intermittent flow, determines the flow rate of fuel supplied to the engine, to ensure that the engine operates properly under all conditions.
2. Description of the Prior Art
Valves of the aforementioned kind have long been known. The main problems of existing valves are the following: the failure to obtain correct proportionality between the excitation frequency of the electromagnetic circuit and the flow rate of fuel delivered by the valve; the difficulty and high cost of constructing the components, which require narrow machining tolerances; and the further difficulty and high cost of assembling the components and installing them in the engine, owing to the dimensions of the injectors.
The object of the invention is to obviate the aforementioned disadvantages by eliminating the two components in existing injectors which are adapted to limit the opening travel of the valve. The first such component, usually a ring secured to the injector body, is traversed by the needle, whereas the second, which comprises a disc-shaped widened portion on the needle, has a diameter greater than the ring aperture. Contact between these two elements defines the end of opening travel, whereas the end of closing travel is defined by contact between a frusto-conical surface on the needle and the opening of the injector, as in the case also of injectors according to the invention.
It is necessary to add metallic material, usually very hard, to ensure that the injector has a long service life, in order to prevent direct contact between the moving iron and the magnetic core. This, however, increases the mass of material in reciprocation and thus increases the response times thereof to the alternating forces which act upon them. This adversely affect the proportional relation between the excitation frequency and the flow rate of injected fuel, as a result of perturbations which will be explained hereinafter.
In the device according to the invention, the masses in reciprocation do not have to bear operating components of the aforementioned kind. Therefore they can be smaller, thus reducing the response time. Another result is that the injector dimensions can be reduced, which is particularly important in single supply installation.
In addition, simplifications are made in the construction, thus reducing the number of tolerances and the cost manufacture.